Do I Use 15-Pound or 30-Pound Paper for a Corrugated Tin Roof?

Differences

• Various factors may affect your decision to use either 15-pound or 30-pound underlayment paper. Contractors use both in a variety of situations with no real difference noted between the two. The 30-pound paper is heavier and can be more durable, but its use is not absolutely necessary when installing your roof. A perusal of the various contractor sites on the Internet reveals that contractors typically use the 15-pound paper, unless they have a specific reason to do otherwise. For example, if local building code requires 30-pound paper, that eliminates the 15-pound paper as a choice.

Repairs

• The 30-pound paper is typically the choice for an underlayment if you are planning to do a repair rather than an installation. Because it is heavier and tends to be more durable, 30-pound paper more effectively eliminates any leaks and prevents future leaks. However, one drawback of doing repairs with either type of paper is that both typically have a self-adhesive backing that can become sticky and cause additional problems during the hot summer months.

Alternatives

• Your underlayment choice is not limited to the use of 15-pound or 30-pound paper. Most contractors use these out of habit or for economic concerns. If you're installing or repairing your own metal roof, however, you can choose an alternative, as some roofers do. Whereas the 15-pound and 30-pound paper is made primarily of asphalt materials, other lightweight papers are made of polymer fibers. These are lighter and easier to install.

Choices

• If you must choose between only the 15-pound and 30-pound paper and cost is not an issue, the 30-pound paper is a logical choice. The 30-pound paper provides a more durable water barrier when the home is undergoing renovations. It also does not tear out as easily if your roof is steep and you need to walk on it to install additional roofing materials. Lightweight paper is less likely to withstand your weight.